1. Field of the Invention
The present invention relates to a process for producing granular activated carbon of high quality from waste tire pyrolysis residues.
2. Description of the Prior Art
The granular activated carbon has been hitherto produced by compounding carbonaceous materials such as coal with binder, shaping to a spherical article, such as granules, carbonizing at 400.degree. to 700.degree. C and activating these materials by contacting with steam at 600.degree. to 1000.degree. C or it has been produced by carbonizing and activating crushed coconut shells in the same manner as described above.
The granular activated carbon is used for absorbing impurities in waste water or gases, and regenerated by heating and used repeatedly.
For this purpose, the granular activated carbon is required to have adsorptive activity and mechanical strength such as compression resistance and abrasion resistance. That is, it is an essential factor for granular activated carbon of high quality to have high degrees of mechanical strength and adsorptive activity even after repeated regeneration operations at a high temperature.
In view of mass production of the granular activated carbon, it is also necessary to establish an efficient method for shaping, carbonizing and activating these raw materials with a high speed and on a large scale.
However, according to conventional processes for producing granular activated carbon, the step of aging treatment, i.e., the step of vaporization of the volatile components slowly by heating at low temperature for several hours or several days, is time-consuming and hinders effective mass production.
On the other hand, the quantity of waste tires has been increasing year after year and they have been recently used for an artificial reef, reclaimed rubber, and reclaimed powder rubber. However, less than half of the waste tires have been consumed for the above mentioned uses. New uses for the waste tires are demanded to solve various troubles caused by the increase of waste tires.
Pyrolysis of waste tires has been recently proposed which produces volatile portions such as gases, light oils and heavy oils used as fuels and further pyrolysis residue is used as raw materials for activated carbon.
When granular activated carbon is produced from the waste tire pyrolysis residue alone, the product has neither excellent mechanical strength nor physical and chemical properties. Unless enough time is taken for an aging treatment, it is very difficult to granulate and form activated carbon having high mechanical strength.
The inventors tried to develop an efficient process for producing granular activated carbon of high quality from the waste tire pyrolysis residue by examining various kinds of additives, binders and the composition ratios and applying various kinds of shaping methods, and succeeded in attaining a novel and efficient method by using a restricted composition by means of a screw extruder under some restricted conditions.
The screw extruder has never been used for producing granular activated carbon because of the difficulty of high speed extrusion owing to high viscosity of the composition of the carbonaceous materials.
Even when the die or the region near the die of the extruder is kept at such high temperatures as those used in the shaping process of conventional plastics, it is not possible to extrude said composition because gas evolution, the intermittent projection of the contents from the die and the breakage of the screw often occur.
These phenomena result from the heterogeneous softening behavior of the composition comprising the carbonaceous material of high melting point and the binder of low melting point.